1. Field of the Invention
The present invention relates to a pixel unit, a method, and a display apparatus comprising the pixel unit. More particularly, the present invention relates to a pixel unit, a method for sensing touch of an object, and a display apparatus comprising the pixel unit.
2. Descriptions of the Related Art
The liquid crystal display (LCD), a full color display device using liquid crystal technology, has many advantages such as low power consumption, low emission, small volume, flexibility in size and a light weight. Therefore, LCD screens have found widespread use in products incorporating display screens, such as digital cameras, personal digital assistants (PDAs) and TV sets. To facilitate the operation of such electronic products incorporating an LCD screen, a touch control function may optionally be provided in a commercially available LCD screen depending on the requirements of the practical applications. The touch control function allows the LCD to read a touch input from a user. This kind of LCD screen is commonly known as a touch control LCD screen.
Generally, a variety of manufacturing methods exist for the commercially available touch control LCD screens. For example, in the capacitive touch control LCD screen, there are two manufacturing methods. The first is to obtain a touch control function by adding a sensing membrane on an LCD screen; while the other is to have a circuit for sensing the touch of an object formed directly into the LCD screen. FIG. 1 is a schematic diagram of a conventional LCD screen that can sense the touch of an object. The LCD screen 1 comprises a pixel unit 10, an output circuit 12 and a plurality of scan lines 14, 16. The pixel unit 10 further comprises a fixed capacitor 100, a liquid crystal capacitor 102, a variable capacitor 104, a pixel switch 106 and a readout switch 108. Once the pixel unit 10 is touched by an object (e.g., a touch pen, a finger or the like), a variation will occur in the capacitance of the variable capacitor 104, and an output current 101 will be generated in response thereto. The output current 101 is transmitted through the readout switch 108 to the output circuit 12, which then determines whether the pixel unit 10 has been touched according to the variation of the output current 101.
In the pixel unit of another conventional LCD screen capable of sensing the touch of an object, the pixel circuit is connected to the output circuit. The pixel unit comprises a fixed capacitor, a liquid crystal capacitor, a plurality of switches, a data line and an output line. The fixed capacitor and the liquid crystal capacitor are configured to receive a common voltage and are connected to these switches. One of these switches is configured to control whether the voltage transmitted by the data line is transmitted to the fixed capacitor and the liquid crystal capacitor. Another switch is configured to control whether the liquid crystal capacitor and the fixed capacitor are connected with the output circuit through the output line. The liquid crystal capacitor is a variable capacitor, the capacitance of which is determined by an equivalent liquid crystal dielectric constant and a distance between the two electrodes thereof. Once the pixel unit is touched by an object, the liquid crystal capacitor will have an increase in the capacitance and the amount of charges it stores will vary accordingly, thus resulting in an output current. In response to this, the output circuit may determine whether the pixel unit has been touched based on the variation of the output current. However, due to the impact of the connection structure described above, voltage transmitted by the data line typically experiences different variations as a function of the different grayscale level displayed by the pixel unit. Consequently, this unfixed voltage may affect the variation of the charge amount stored by the liquid crystal capacitor, thus making it difficult for the output circuit to determine whether the pixel unit has been touched.
According to aforementioned descriptions, the conventional capacitive touch control LCD screens all require additional elements in the original LCD screens. Since a sensing element and readout line have to be added into the pixel, the open ratio of the pixel unit tends to be decreased. However, the conventional pixel unit is susceptible to impact from the voltage input of the data line, which makes it difficult to determine whether the pixel has been touched. Therefore, efforts still have to be made in the art to provide a capacitive touch control LCD screen that can reduce the cost and improve the sensing ability without modifying the structure and circuit of the conventional pixel units.